This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. A key step in the Wood-Ljungdahl carbon fixation pathway is the transfer of a methyl group from methyltetrahydrofolate, bound by a methyltransferase (MeTr), to the corrinoid ring of the corrinoid iron[unreadable]sulfur protein (CFeSP). Separate crystal structures of MeTr and CFeSP have not been sufficient in explaining how the methyl transfer reaction takes place;therefore, we seek to shed light on this methyl hand-off by obtaining a crystal structure of these proteins in complex.